The ITEM-1 mAb reacts with human TWEAK Receptor/Fn14 (fibroblast growth factor-inducible 14kDa protein). Fn14 is distantly related to the TNFR family, containing one cysteine-rich domain in the extracellular region and a TNFR-associated factor binding domain but does not contain a death domain (DD) cytoplasmic region. Fn14 plays a role in TWEAK-induced endothelial cell migration, proliferation, and angiogenesis. TWEAK-induced cell death via Fn14 includes both apoptosis and necrosis and can be blocked by an anti-TWEAK antibody, CARL-1. Fn14 is expressed on HUVEC and in some cancer tissues but not on freshly isolated PBMCs. Fn14 mRNA expression has been identified during liver regeneration.